We present spectra of 5 ultra-diffuse galaxies ( UDGs ) in the vicinity of the Coma Cluster obtained with the Multi-Object Double Spectrograph on the Large Binocular Telescope .
We confirm 4 of these as members of the cluster , quintupling the number of spectroscopically confirmed systems .
Like the previously confirmed large ( projected half light radius > 4.6 kpc ) UDG , DF44 , the systems we targeted all have projected half light radii > 2.9 kpc .
As such , we spectroscopically confirm a population of physically large UDGs in the Coma cluster .
The remaining UDG is located in the field , about 45 Mpc behind the cluster .
We observe Balmer and Ca II H & K absorption lines in all of our UDG spectra .
By comparing the stacked UDG spectrum against stellar population synthesis models , we conclude that , on average , these UDGs are composed of metal-poor stars ( [ Fe/H ] \lesssim - 1.5 ) .
We also discover the first UDG with [ OII ] and [ OIII ] emission lines within a clustered environment , demonstrating that not all cluster UDGs are devoid of gas and sources of ionizing radiation .